Has anyone tried to lighten the rear subframe? I'm thinking of smoothing out the inside of the rails and reducing the size of all the massive mounts on it..
Any advice or pictures?

The lower rails on the tail can come out completely. Just don't carry a passenger after you do that. A few thousand miles on my gen1 without the lower rails and no problems. I have seen a pic of a drag bike that had extra lightening holes in the rails below the seat. The guy continued a hole pattern like the access hole for adjusting the rear suspension.

I have already removed the lower bars and installed aluminum bolts, only using one lock, and I've moved the ecu so that it's next to the forward fuse block.
Guess I'll take the subframe off and see what comes to mind.

the bolts by the main frame are very tight. It may be a star hex key that you need to take thoseout. I tried a regular hex and they were not buging plus the key stuck in the bolts. Get the bike good and hot before trying to remove and be sure you have the right hex key. Could try a heat gun if your careful to not damage the paint. There is factory locktite in there and they are torqued.